A hose for automotive fuel piping having a fluororesin layer as a gasoline barrier is now being highlighted in accordance with the strengthening of SHED (Sealed Housing for Evaporative Determinations) in the United States. Japanese Patent Laid-Open No. 5-44874/1993 discloses a hose structure in which a fluororesin having a low gasoline permeability, such as tetrafluoroethylene/ethylene copolymer or polytetrafluoroethylene, is used as an inner layer and an epichlorohydrin rubber as an outer layer. In the formation of this structure, the surface of the inner layer resin was treated by corona discharge or UV irradiation and bonded to the outer layer rubber with a thermosetting adhesive which is gasoline-resistant, flexible and thermally stable. Further, Japanese Patent Laid-Open No. 6-99548/1994 discloses a hose structure in which a fluororesin such as polyvinylidene fluoride or polychlorotri-fluoroethylene is used as an inner layer and a rubber elastomer such as nitrile/butadiene rubber or epichlorohydrin rubber as an outer layer. In this reference, there is no particular description on the bonding of the inner layer resin to the outer layer rubber. However, it is conceivable that, eventually, a modification to achieve a better bonding through surface treatment such as corona discharge cannot but be effected because no satisfactory bonding strength can be attained between the fluororesin and the rubber elastomer such as NBR rubber by the conventional vulcanization bonding.
Further, Japanese Patent Publication No. 59-38896/1984 discloses that, in a structure composed of a fluororubber which is a terpolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene as an inner layer and an epichlorohydrin rubber as an outer layer, the incorporation of a divalent metal oxide or hydroxide, a fluorinated polyhydroxy compound and an organic compound containing a nitrogen or phosphorus atom in its molecule as common vulcanization system components remarkably improves the bonding between the layers having inherently a problem in lamination attributed to poor compatibility between the two types of rubbers and vulcanization systems different from each other.
Japanese Patent Publication No. 60-33663/1985 teaches the addition of a 1,8-diaza-bicylco(5.4.0)undecene-7 salt of a carboxylic acid to a structure composed of a fluoro-rubber as an inner layer and an epichlorohydrin rubber as an outer layer and Japanese Patent Publication No. 5-214118/1993 shows the interposition of a phosphonium salt between the rubber layers in the production of a laminate composed of the fluororubber layer and the other rubber layer.
All the above-mentioned fluororesins were hard and lacked flexibility, so that, when molded into hoses, the handling thereof was very difficult. Moreover, these hoses had a drawback in securing the sealing at the junctions where other pipes were inserted into the hoses. Further, surface treatment such as corona discharge over the entire inner surface of a long-hose-shaped fluororesin layer was so difficult that the formation of a rubber layer as an innermost layer which was desired for improving the sealing properties encountered difficulties.